[FFmpeg-devel] Fixpoint FFT optimization, with MDCT and IMDCT wrappers for audio optimization

[Michael Niedermayer]

On Sat, Jul 28, 2007 at 08:49:52PM -0400, Marc Hoffman wrote:
> On 7/27/07, Michael Niedermayer <michaelni at gmx.at> wrote:
> > Hi
> >
> > On Fri, Jul 27, 2007 at 09:56:34PM -0400, Marc Hoffman wrote:
> > > Hi,
> > >
> > > On 7/27/07, Michael Niedermayer <michaelni at gmx.at> wrote:
> > > > Hi
> > > >
> > > > On Fri, Jul 27, 2007 at 05:40:14PM -0400, mmh wrote:
> > > > [...]
> > > > > +/*
> >
> > >
> > > >
> > > > also several iterations have trivial (1/-1/0) w* these should not be done
> > > > in this generic way
> > > ?
> >
> > these things called twiddle factors, which are represented by wwr and wwi in
> > your code have values like 1/-1/0, well 32768/-32768/0 as its fixedpoint
> > in some iterations and its very lame to do a full complex multiplication
> > for w being one of 1,-1,i,-i
> >
> 
> So you want to see the trivial stage pulled?  Is the use of N/2
> acceptable to you here?

no, N>>1 is better


[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

In a rich man's house there is no place to spit but his face.
-- Diogenes of Sinope
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 189 bytes
Desc: not available
URL: <http://lists.mplayerhq.hu/pipermail/ffmpeg-devel/attachments/20070729/6866ceae/attachment.pgp>